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[en] Background: In luminescence dating, dose rate is the irradiation dose a sample absorbed per unit time. The estimation of a dose rate affects the reliability of the burial age. Quadratic Propagation of Uncertainty (QPU) is routinely used to assess the standard error of a dose rate estimate. However, dose rate calculation involves lots of non-linear transformations between various parameters. This complicates the application of QPU method in dose rate error estimation. Purpose: In the current study, a detailed introduction to the calculation of the annual dose rate in case of coarse quartz sediments is given. A Monte Carlo technique (a 'parametric bootstrap' method) is employed to simulate the propagation of uncertainty in dose rate calculation. Methods: An open source R program used for performing the simulation is developed. A practical application of this technique is illustrated using a measured data set. Results and Conclusion: The Monte Carlo method is more flexible and simple in comparison with the QPU approach in dose rate error assessment. The stochastic scheme described in this article can be applied to any field of the analytical sciences. (authors)
[en] The characteristics of eolian sand activity are greatly influenced by the wind regime, and wind regimes have been changing around the world in response to climate change. This has also been true in the desert area of northwestern China since 1965, and these changes have changed the region’s landforms, sandstorm frequency, and desertification. In this study, we analyzed the temporal and spatial variation of the region’s near-surface wind field since 1965. We found an average annual wind speed during this period of 1.7 m s−1, with a decreasing trend from 1965 to 2000 and an increasing trend from 2000 to 2015. The maximum rate of decrease occurred in the spring and in the eastern Taklimakan Desert. The variation of the average wind speed depended on the frequency of winds strong enough to entrain sand (with a wind speed > 6 m s−1). We also found that variations of the drift potential were primarily controlled by three prevailing wind groups (winds from the northwest, north, and northeast), but showed complex changes between seasons and regions. The wind direction in the Taklimakan Desert is characterized by two characteristics of branch and steering, the branch line is swinging in the direction of the east and the west (81.5° E~84° E). The changes in wind speed were mainly caused by a decreased frequency of strong winds, precipitation, and urban development. However, the variation of wind speed had less impact on the desert environment than the variation of wind direction.
[en] Research on the wind environment variation improves our understanding of the process of climate change. This study examines temporal variation of the near-surface wind environment and investigates its possible causes in the Mu Us Dunefield of Northern China from 1960 to 2014, through analyzing the meteorological data from seven stations and the land use and land cover (LUCC) change data with 100 m resolution. The wind speed had a widespread significant decrease with an average trend of − 0.111 m s−1 decade−1, although the rate of decrease differed seasonally. This negative trend was also found in the winds that were above a 5 m s−1 threshold, as well as the percentage of their days, which influenced the wind speed change more strongly. Overall, 88.69% of the annual decrease resulted from decreases in the maximum wind speed, and the percentage even reached 100% in autumn and winter. We further found that the drift potential decreased at decadal time scales, mainly focusing on three prevailing wind groups: the northerly, westerly, and southerly winds. This revealed the weakened East Asian monsoon and westerly circulation in the lower atmosphere. Against the context of climate warming, the decline of wind speeds in spring was closely related to the greenhouse gas, while the winter decline was closely associated with the aerosol or atmospheric dust. Moreover, the LUCC change showed the decreased areas of sand land and the increased areas of vegetation-covered land, which increased the ground surface roughness and was another reason for the weakened wind environment.
[en] Highlights: • Shear horizontal wave dispersion in nanolayers with surface effects is examined. • Wave velocity is dependent on the layer thickness and surface elastic constants. • Surface elastic constants can be analytically derived from the wave velocity. - Abstract: In this work, the shear horizontal (SH) wave dispersion in two dissimilar nanolayers is investigated by using the surface elasticity theory in which the surface effects are featured by surface elastic constants. It is found that the SH wave dispersion shows distinct dependence on the nanolayer thickness as well as the surface elastic constants. The larger the surface elastic modulus and/or the smaller the thickness, the higher the phase velocity. In particular, as the wave frequency approaches zero, the analytical relation between the phase velocity in the first mode dispersion and the surface elastic constants is deduced. Thereby, a facile method is suggested to determine the surface elastic constants from the phase velocity of SH waves scattered in nanolayers.